Electric stimulation of neural tissue is used to treat a variety of disorders. Specifically, leadable electric stimulators and leads have been used to treat chronic pain, muscular disorders, hearing problems, symptoms of Parkinson's Disease, bladder control, and sexual dysfunction, among others. Often, a lead terminating in electrodes is situated close to region of interest, the stimulation of which is expected to alleviate the condition of the patient, in a tissue such as spinal cord, nerve roots, muscles, or brain tissue. A leaded signal generator (IPG) connected to the lead is then used to generate patterns of electric pulses that stimulate the tissue.
However, the applied stimulation might also affect tissue at the proximity of the region of interest, and such stimulation might cause unwanted side-effects.
U.S. Pat. No. 7,047,084, the contents of which are incorporated herein by reference, describes an apparatus for providing controlled and directional stimulation patterns for tissue stimulation. The apparatus includes a leadable pulse generator connected to a lead. The lead has electrodes placed about a perimeter. In addition, the lead may include electrodes placed longitudinally along the axis of the lead. This patent suggests that by applying charge differences between circumferentially distributed electrodes, a smaller stimulation field may be established. In addition, the patent suggests that by stimulating between electrodes distributed longitudinally on the same side of a lead, a directional flow field may be established.
U.S. Pat. No. 5,895,416, the contents of which are incorporated herein by reference, describes an electric field steering assembly. The assembly comprises a pulse generator coupled to at least one leaded lead. The lead has at its distal end at least three spaced apart electrodes, and electrical circuitry for adjusting the current and/or voltage at each electrode.
U.S. Pat. No. 6,988,006 discusses creating and steering a supra-threshold stimulation by controlling a time-delay between two sub-threshold stimulations, such that the two stimulations overlap to provide supra-threshold stimulation and changing the time-delay changes the location of the supra-threshold stimulation.